To commit suicide. Reference comes from online video games, where a player quits the game when they are tired of playing or disillusioned with their suckage.

In these games, such as Call of Duty (pre modern warfare 2), one of the players in the game is randomly and unknowingly given the host connection. If this player leaves the game, it ends the match for everyone :(

When a player is fed up and tired of getting owned, they may decide to leave the game. When doing so, one might exclaim they are going to "find out if they are the host", referring to the possible outcome when they leave the game and as a result the game ends for all the players.

The term refers to committing suicide, as in similar frustration when leaving a video game.

(In game) " Wow, i have died 36 times in a row and I can't get a kill. The enemy team is just a bunch of camping snipers. This connection sucks ass, i'm lagging all over the place. Im about the find out if im the host"

(real life application)

"Yo bro, I just got a 15 on that math test, I'm about to find out if I'm the Host"

"Wow some kid just walked over to me and said 'safety', i'm about to find out if i'm the Host"

"My best friend has been secretly sleeping with my girlfriend for 3 months now. Im about to find out if Im the Host"